Droplet generator and method of servicing extreme ultraviolet radiation source apparatus

ABSTRACT

An extreme ultraviolet radiation source apparatus includes a chamber including at least a droplet generator, a nozzle of the droplet generator, and a dry ice blasting assembly. The droplet generator includes a reservoir for a molten metal, and the nozzle has a first end connected to the reservoir and a second opposing end where molten metal droplets emerge from the nozzle. The dry ice blasting assembly includes a blasting nozzle, a blasting air inlet and a blaster carbon dioxide (CO2) inlet. The blasting nozzle is disposed inside the chamber. The blasting nozzle is arranged to direct a pressurized air stream and dry ice particles at the nozzle of the droplet generator.

RELATED APPLICATION

This application is a Continuation Application of U.S. patentapplication Ser. No. 16/933,872 filed Jul. 20, 2020, now U.S. Pat. No.11,029,613, which is a Continuation Application of U.S. patentapplication Ser. No. 16/404,235 filed May 6, 2019, now U.S. Pat. No.10,719,020, which claims priority to U.S. Provisional Patent ApplicationNo. 62/692,565 filed on Jun. 29, 2018, the entire contents of each ofwhich are incorporated herein by reference.

BACKGROUND

As consumer devices have gotten smaller and smaller in response toconsumer demand, the individual components of these devices havenecessarily decreased in size as well. Semiconductor devices, which makeup a major component of devices such as mobile phones, computer tablets,and the like, have been pressured to become smaller and smaller, with acorresponding pressure on the individual devices (e.g., transistors,resistors, capacitors, etc.) within the semiconductor devices to also bereduced in size. The decrease in size of devices has been met withadvancements in semiconductor manufacturing techniques such aslithography.

For example, the wavelength of radiation used for lithography hasdecreased from ultraviolet to deep ultraviolet (DUV) and, more recentlyto extreme ultraviolet (EUV). Further decreases in component sizerequire further improvements in resolution of lithography which areachievable using extreme ultraviolet lithography (EUVL). EUVL employsradiation having a wavelength of about 1-100 nm.

As the semiconductor industry has progressed into nanometer technologyprocess nodes in pursuit of higher device density, higher performance,and lower costs, there have been challenges in reducing semiconductorfeature size.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detaileddescription when read with the accompanying figures. It is emphasizedthat, in accordance with the standard practice in the industry, variousfeatures are not drawn to scale and are used for illustration purposesonly. In fact, the dimensions of the various features may be arbitrarilyincreased or reduced for clarity of discussion.

FIG. 1 shows an extreme ultraviolet lithography tool according to anembodiment of the disclosure.

FIG. 2 shows a schematic diagram of a droplet generator according to anembodiment of the disclosure.

FIG. 3 shows a detailed view of a droplet generator according to anembodiment of the disclosure.

FIG. 4 shows a detailed view of a droplet generator nozzle according toan embodiment of the disclosure.

FIGS. 5A-5B show schematic diagrams of generating a droplet by a dropletgenerator according to an embodiment of the disclosure.

FIG. 5C shows a schematic diagram of a method of cleaning a dropletgenerator according to an embodiment of the disclosure.

FIG. 6 shows a detailed view of a dry ice blasting assembly according toan embodiment of the disclosure.

FIG. 7 shows a detailed view of a dry ice blasting assembly according toanother embodiment of the disclosure.

FIG. 8 shows a flow chart of a method of cleaning a droplet generator ofan EUV radiation source apparatus according to an embodiment of thedisclosure.

FIG. 9 shows a flow chart of a method of cleaning the droplet generatorof the EUV radiation source apparatus according to another embodiment ofthe disclosure.

DETAILED DESCRIPTION

It is to be understood that the following disclosure provides manydifferent embodiments, or examples, for implementing different featuresof the disclosure. Specific embodiments or examples of components andarrangements are described below to simplify the present disclosure.These are, of course, merely examples and are not intended to belimiting. For example, dimensions of elements are not limited to thedisclosed range or values, but may depend upon process conditions and/ordesired properties of the device. Moreover, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed interposing the first and second features, suchthat the first and second features may not be in direct contact. Variousfeatures may be arbitrarily drawn in different scales for simplicity andclarity.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The device may be otherwise oriented (rotated 90 degrees orat other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly. In addition, the term“made of” may mean either “comprising” or “consisting of.”

The present disclosure is generally related to extreme ultraviolet (EUV)lithography systems and methods. More particularly, it is related toextreme ultraviolet lithography (EUVL) tools and methods of servicingthe tools. In an EUVL tool, a laser-produced plasma (LPP) generatesextreme ultraviolet radiation which is used to image a photoresistcoated substrate. In an EUV tool, an excitation laser heats metal (e.g.,tin, lithium, etc.) target droplets in the LPP chamber to ionize thedroplets to plasma which emits the EUV radiation. For reproduciblegeneration of EUV radiation, the target droplets arriving at the focalpoint (also referred to herein as the “zone of excitation”) have to besubstantially the same size and arrive at the zone of excitation at thesame time as an excitation pulse from the excitation laser arrives.Thus, stable generation of target droplets that travel from the targetdroplet generator 115 to the zone of excitation at a uniform (orpredictable) speed contributes to efficiency and stability of the LPPEUV radiation source. Any instability in the generation of targetdroplets can impact the EUVL tool performance, and in some cases, forexample, if the nozzle 120 of the droplet generator 115 is clogged, thetool may have to be shut down to repair (e.g., unclog the nozzle 120)the droplet generator 115. Additionally, when refilling the dropletgenerator 115, there is a possibility of oxidation of tin, which cancause clogging of the nozzle 120. In such cases of a clogged nozzle 120,the entire droplet generator 115 needs to be changed, causing longdowntime for the EUVL tool. Embodiments of the present disclosureprovide for an apparatus and methods for cleaning and/or unclogging adroplet generator 115 without removing the droplet generator 115 fromthe EUVL tool. In other words, the presently disclosed embodimentsenable in-line cleaning and/or unclogging of the droplet generator 115.

FIG. 1 is a schematic view of an EUV lithography tool with a laserproduction plasma (LPP) based EUV radiation source, constructed inaccordance with some embodiments of the present disclosure. The EUVlithography system includes an EUV radiation source 100 to generate EUVradiation, an exposure device 200, such as a scanner, and an excitationlaser source 300. As shown in FIG. 1 , in some embodiments, the EUVradiation source 100 and the exposure device 200 are installed on a mainfloor MF of a clean room, while the excitation laser source 300 isinstalled on a base floor BF located under the main floor. Each of theEUV radiation source 100 and the exposure device 200 are placed overpedestal plates PP1 and PP2 via dampers DP1 and DP2, respectively. TheEUV radiation source 100 and the exposure device 200 are coupled to eachother by a coupling mechanism, which may include a focusing unit.

The EUV lithography tool is designed to expose a resist layer by EUVlight (also interchangeably referred to herein as EUV radiation). Theresist layer is a material sensitive to the EUV light. The EUVlithography system employs the EUV radiation source 100 to generate EUVlight, such as EUV light having a wavelength ranging between about 1 nmand about 100 nm. In one particular example, the EUV radiation source100 generates an EUV light with a wavelength centered at about 13.5 nm.In the present embodiment, the EUV radiation source 100 utilizes amechanism of laser-produced plasma (LPP) to generate the EUV radiation.

The exposure device 200 includes various reflective optic components,such as convex/concave/flat mirrors, a mask holding mechanism includinga mask stage, and wafer holding mechanism. The EUV radiation EUVgenerated by the EUV radiation source 100 is guided by the reflectiveoptical components onto a mask secured on the mask stage. In someembodiments, the mask stage includes an electrostatic chuck (e-chuck) tosecure the mask.

As used herein, the term “optic” is meant to be broadly construed toinclude, and not necessarily be limited to, one or more components whichreflect and/or transmit and/or operate on incident light, and includes,but is not limited to, one or more lenses, windows, filters, wedges,prisms, grisms, gratings, transmission fibers, etalons, diffusers,homogenizers, detectors and other instrument components, apertures,axicons and mirrors including multi-layer mirrors, near-normal incidencemirrors, grazing incidence mirrors, specular reflectors, diffusereflectors and combinations thereof. Moreover, unless otherwisespecified, neither the term “optic”, as used herein, are meant to belimited to components which operate solely or to advantage within one ormore specific wavelength range(s) such as at the EUV output lightwavelength, the irradiation laser wavelength, a wavelength suitable formetrology or any other specific wavelength.

Because gas molecules absorb EUV light, the lithography system for theEUV lithography patterning is maintained in a vacuum or a low pressureenvironment to avoid EUV intensity loss.

In the present disclosure, the terms mask, photomask, and reticle areused interchangeably. In the present embodiment, the patterning optic isa reflective mask. In an embodiment, the reflective mask includes asubstrate with a suitable material, such as a low thermal expansionmaterial or fused quartz. In various examples, the material includesTiO₂ doped SiO₂, or other suitable materials with low thermal expansion.The reflective mask includes multiple reflective multiple layers (ML)deposited on the substrate. The ML includes one or more film pairs, suchas molybdenum-silicon (Mo/Si) film pairs (e.g., a layer of molybdenumabove or below a layer of silicon in each film pair). Alternatively, theML may include molybdenum-beryllium (Mo/Be) film pairs, or othersuitable materials that are configured to highly reflect the EUV light.The mask may further include a capping layer, such as ruthenium (Ru),disposed on the ML for protection. The mask further includes anabsorption layer, such as a tantalum boron nitride (TaBN) layer,deposited over the ML. The absorption layer is patterned to define alayer of an integrated circuit (IC). Alternatively, another reflectivelayer may be deposited over the ML and is patterned to define a layer ofan integrated circuit, thereby forming an EUV phase shift mask.

The EUVL tool further includes other modules or is integrated with (orcoupled with) other modules in some embodiments.

As shown in FIG. 1 , the EUV radiation source 100 includes a targetdroplet generator 115 and a LPP collector 110, enclosed by a chamber105. In various embodiments, the target droplet generator 115 includes areservoir 150 (see FIG. 3 ) to hold a source material and a nozzle 120through which target droplets DP of the source material are suppliedinto the chamber 105. The EUV radiation source 100 may further include adry ice blasting assembly 1000 that includes a blasting member 1100 andan exhaust member 1200 selectively attachable to and extendable from thechamber 105. FIG. 1 illustrates an exemplary configuration of the dryice blasting assembly 1000. However, any appropriate configuration suchas size, shape, and location with respect to the chamber 105 iscontemplated and is not limited in this regard.

In some embodiments, the target droplets DP are droplets of tin (Sn),lithium (Li), or an alloy of Sn and Li. In some embodiments, the targetdroplets DP each have a diameter in a range from about 10 microns (μm)to about 100 μm. For example, in an embodiment, the target droplets DPare tin droplets, having a diameter of about 10 μm to about 100 μm. Inother embodiments, the target droplets DP are tin droplets having adiameter of about 25 μm to about 50 μm. In some embodiments, the targetdroplets DP are supplied through the nozzle 120 at a rate in a rangefrom about 50 droplets per second (i.e., an ejection-frequency of about50 Hz) to about 50,000 droplets per second (i.e., an ejection-frequencyof about 50 kHz). In some embodiments, the target droplets DP aresupplied at an ejection-frequency of about 100 Hz to a about 25 kHz. Inother embodiments, the target droplets DP are supplied at an ejectionfrequency of about 500 Hz to about 10 kHz. The target droplets DP areejected through the nozzle 120 and into a zone of excitation ZE at aspeed in a range of about 10 meters per second (m/s) to about 100 m/s insome embodiments. In some embodiments, the target droplets DP have aspeed of about 10 m/s to about 75 m/s. In other embodiments, the targetdroplets have a speed of about 25 m/s to about 50 m/s.

Referring back to FIG. 1 , an excitation laser LR2 generated by theexcitation laser source 300 is a pulse laser. The laser pulses LR2 aregenerated by the excitation laser source 300. The excitation lasersource 300 may include a laser generator 310, laser guide optics 320 anda focusing apparatus 330. In some embodiments, the laser source 310includes a carbon dioxide (CO₂) or a neodymium-doped yttrium aluminumgarnet (Nd:YAG) laser source with a wavelength in the infrared region ofthe electromagnetic spectrum. For example, the laser source 310 has awavelength of 9.4 μm or 10.6 μm, in an embodiment. The laser light LR1generated by the laser generator 300 is guided by the laser guide optics320 and focused into the excitation laser LR2 by the focusing apparatus330, and then introduced into the EUV radiation source 100.

In some embodiments, the excitation laser LR2 includes a pre-heat laserand a main laser. In such embodiments, the pre-heat laser pulse(interchangeably referred to herein as the “pre-pulse) is used to heat(or pre-heat) a given target droplet to create a low-density targetplume with multiple smaller droplets, which is subsequently heated (orreheated) by a pulse from the main laser, generating increased emissionof EUV light.

In various embodiments, the pre-heat laser pulses have a spot size about100 μm or less, and the main laser pulses have a spot size in a range ofabout 150 μm to about 300 μm. In some embodiments, the pre-heat laserand the main laser pulses have a pulse-duration in the range from about10 ns to about 50 ns, and a pulse-frequency in the range from about 1kHz to about 100 kHz. In various embodiments, the pre-heat laser and themain laser have an average power in the range from about 1 kilowatt (kW)to about 50 kW. The pulse-frequency of the excitation laser LR2 ismatched with the ejection-frequency of the target droplets DP in anembodiment.

The laser light LR2 is directed through windows (or lenses) into thezone of excitation ZE. The windows adopt a suitable materialsubstantially transparent to the laser beams. The generation of thepulse lasers is synchronized with the ejection of the target droplets DPthrough the nozzle 120. As the target droplets move through theexcitation zone, the pre-pulses heat the target droplets and transformthem into low-density target plumes. A delay between the pre-pulse andthe main pulse is controlled to allow the target plume to form and toexpand to an optimal size and geometry. In various embodiments, thepre-pulse and the main pulse have the same pulse-duration and peakpower. When the main pulse heats the target plume, a high-temperatureplasma is generated. The plasma emits EUV radiation, which is collectedby the collector mirror 110. The collector 110 further reflects andfocuses the EUV radiation for the lithography exposing processesperformed through the exposure device 200. The droplet catcher 125 isused for catching excessive target droplets. For example, some targetdroplets may be purposely missed by the laser pulses.

Referring back to FIG. 1 , the collector 110 is designed with a propercoating material and shape to function as a mirror for EUV collection,reflection, and focusing. In some embodiments, the collector 110 isdesigned to have an ellipsoidal geometry. In some embodiments, thecoating material of the collector 100 is similar to the reflectivemultilayer of the EUV mask. In some examples, the coating material ofthe collector 110 includes a ML (such as one or more Mo/Si film pairs)and may further include a capping layer (such as Ru) coated on the ML tosubstantially reflect the EUV light. In some embodiments, the collector110 may further include a grating structure designed to effectivelyscatter the laser beam directed onto the collector 110. For example, asilicon nitride layer is coated on the collector 110 and is patterned tohave a grating pattern.

As shown in FIG. 1 , in the present embodiment, a buffer gas is suppliedfrom a first buffer gas supply 130 through the aperture in collector 110by which the pulse laser is delivered to the tin droplets. In someembodiments, the buffer gas is H₂, He, Ar, N₂ or another inert gas. Incertain embodiments, H radicals generated by ionization of the H₂ buffergas is used for cleaning purposes. The buffer gas can also be providedthrough one or more second buffer gas supplies 135 toward the collector110 and/or around the edges of the collector 110. Further, the chamber105 includes one or more gas outlets 140 so that the buffer gas isexhausted outside the chamber 105.

Hydrogen gas has low absorption to the EUV radiation. Hydrogen gasreaching the coating surface of the collector 110 reacts chemically witha metal of the droplet forming a hydride, e.g., metal hydride. When tin(Sn) is used as the droplet, stannane (SnH₄), which is a gaseousbyproduct of the EUV generation process, is formed. The gaseous SnH₄ isthen pumped out through the outlet 140.

FIG. 2 illustrates the components of the droplet generator 115 inschematic format. As shown there, the droplet generator 115 includes areservoir 150 holding a fluid 145, e.g. molten tin, under pressure P.The reservoir 150 is formed with an orifice 155 allowing the pressurizedfluid 145 to flow through the orifice 155 establishing a continuousstream which subsequently breaks into one or more droplets DP1, DP2exiting the nozzle 120.

The target droplet generator 115 shown further includes a sub-systemproducing a disturbance in the fluid 145 having an electro-actuatableelement 160 that is operably coupled with the fluid 145 and a signalgenerator 165 driving the electro-actuatable element 160 in someembodiments. In some embodiments, the electro-actuatable element 160 isa piezoelectric actuator that applies vibration to the fluid 145. Insome embodiments, the electro-actuatable element 160 is an ultrasonictransducer or a megasonic transducer.

A detailed cross section view of the droplet generator 115 according toan embodiment is shown in FIG. 3 . The droplet generator 115 includes areservoir 150 containing the molten metal 145 and nozzle 120 at the endof the reservoir 150.

In some embodiments, the nozzle 120 is maintained at a certaintemperature that is higher than the melting point of the sourcematerial. However, under certain conditions such as, for example, if thechamber 105 is vented for a service or if there is an unscheduled changein temperature of the chamber 105, temperature of the nozzle 120 may bereduced to below the melting point of the source material, e.g., tin.When the nozzle 120 cools down, liquid source material may leak throughthe nozzle 120 because of particulate formation at the nozzle 120. Theleaked source material may be deposited on the collector 110 resultingin a reduction in the reflectivity of the collector 110. This in turnresults in the loss of stability and efficiency of the EUV radiationsource 100. In some cases, replacement of the collector 110 may berequired, leading to unnecessary and avoidable expense as well asdown-time for the entire lithography system.

In addition, if the chamber 105 is vented the molten source material mayreact with oxygen in the ambient resulting in the formation of metaloxide particulate contamination. For example, molten tin may react withoxygen forming tin oxide solid particles. The tin oxide particles cancoat optical surfaces in the EUVL tool. The metal oxide particles mayalso clog the nozzle 120 interfering with subsequent droplet flow whenthe EUVL tool is restarted.

FIG. 4 shows a detailed view of a droplet generator nozzle 120 accordingto an embodiment of the disclosure. The outer body 190 of the nozzle 120is made of a metal, such as titanium or stainless steel in someembodiments. The tip 195 of the nozzle 120, where the droplets DP aregenerated, is constituted by a strong, non-fragile, material in someembodiments, for example a metal (e.g., titanium), a ceramic, silicon ora silicon based compound, such as silicon nitride. The tip 195 of thenozzle 120 is made of a material that can withstand the temperaturesrequired to maintain the target metal in the molten state and not reactwith molten target metal 1020. In some embodiments, the tip 195 of thenozzle 120 is made of silicon coated with silicon nitride. Such a tip195 of the nozzle 120 is able to withstand high pressures within thenozzle 120, and therefore, high gas pressures can be used to force themolten metal through the nozzle 120.

An isolation valve 185 is located at the end of the nozzle 120. Theisolation valve 185 is open during operation of the droplet generator115. When maintenance or servicing of the radiation source 100 isrequired, the isolation valve 185 closes to seal the nozzle 120. Thechamber 105 of the EUV radiation source 100 is maintained under vacuumor low pressure during operation of the EUVL tool. Because EUV light isabsorbed by most materials, including gases, it is necessary to operatethe EUV tool under low pressure or vacuum to prevent loss of exposurelight energy during imaging operations.

The vacuum chamber 105 may be opened when it is necessary to performmaintenance or service the EUVL tool. Exposing the vacuum chamber 105 tothe ambient atmosphere introduces oxygen, which readily reacts withheated metals to form metal oxides. For example, the oxygen may reactwith molten tin in the nozzle 120 of the droplet generator 115 to formtin oxides, such as stannous oxide (SnO) and stannic oxide (SnO₂). Insome embodiments, the molten tin is maintained at a temperature of about250° C. At this temperature tin oxides are solid. Thus, any tin oxidesthat would form would precipitate out of the molten tin. When suchcleaning is required, and in particular if the molten tin results inclogging of the droplet generator nozzle 120, the droplet generator 115may need to be removed from the EUVL tool. This can cause undesirablelong downtimes.

FIG. 5A shows an exemplary stable generation of target droplets DP1,DP2. The target droplets travel from the target droplet generator 115 inthe EUV radiation source 100 to the zone of excitation at a uniform (orpredictable) speed that contributes to an efficiency and stability ofthe EUV radiation source 100. The target droplets DP1, DP2 aresubstantially the same size. As shown in FIG. 5B, the nozzle 120 of thedroplet generator 115 may be clogged by a residual material 1022, forexample, molten target metal 1020. The target droplets DP1, DP2 are notthe same size. In some embodiments, although the target droplets DP1,DP2 are substantially the same size, the target droplets DP1, DP2 maynot arrive at the zone of excitation at a desired timing due to theresidual material 1022.

Referring to FIG. 5C, the EUV radiation source apparatus 100 accordingto the present disclosure includes a dry ice blasting assembly 1000selectively attachable to and extendable from the chamber 105. The dryice blasting assembly 1000 includes the blasting member 1100 and theexhaust member 1200 selectively attachable to and extendable from thechamber 105. The blasting member 1100 is configured to directpressurized dry ice (CO₂) particles 1080 to the droplet generator 115 toclean the nozzle 120 and to remove the residual material 1022. Theexhaust member 1200 collects the residual material 1022 separated fromthe nozzle 120 of the droplet generator 115 and gaseous carbon dioxide1088 sublimated from the solid dry ice particles 1082 through an exhaustline 1220.

With respect to FIG. 6 , in some embodiments, the dry ice blastingassembly 1000 includes a blasting air inlet 1120, a blaster carbondioxide (CO₂) inlet 1130, a blasting mixer 1140 and a blasting nozzle1150. In a particular embodiment, the blasting nozzle 1150 furtherincludes a pulsation insert 1160 and a directional insert 1170. Thepulsation insert 1160 is configured to generate a pulsation/oscillationof the pressurized air stream 1084 by inserting a mechanical device intothe blasting nozzle 1150. The directional insert 1170 is configured tochange a two-dimensional direction and/or three-dimensional rotation ofthe pressurized air stream 1084 by inserting a mechanical device intothe blasting nozzle 1150.

Some embodiments of the dry ice blasting assembly 1000 further includean extendable positioner 1180. The extendable positioner 1180 “pops-up”from the chamber 105 when needed and is substantially concealed withinthe chamber 105 when not in use. A controller 1500 selectively enables atelescopingly extendable portion 1182 of the extendable positioner 1180in some embodiments. The telescopingly extendable portion 1182 includesa cylindrical body 1184 that is coaxially slideably received within thechamber 105 and has an inwardly projecting annular flange 1186 whichbears against any appropriate type of sealing.

In certain embodiments, the extendable positioner 1180 is a 3-axisrotational device, and when it rotates in a direction, the blastingnozzle 1150 attached to the extendable positioner 1180 is moved to acleaning position.

In some embodiments, the controller 1500 is configured to monitorresidual material 1022 on the droplet generator by a monitoring device1520, adjust valves of the blasting pump when an amount of residualmaterial 1022 in the droplet generator is more than a threshold amount,and regulate ejecting parameters of the dry ice particles by operatingthe blasting compressor and the blasting pump when the pressurized dryice particles are ejected from the blasting nozzle. In some embodiments,the monitoring device is a camera. In some embodiments, the ejection ofthe pressurized dry ice particles from the blasting nozzle is stoppedwhen the monitoring device detects the amount of the residual materialon the droplet generator is below the threshold amount. Any appropriatecontrolling configuration regarding automatic and/or manual operation iscontemplated and is not limited in this regard.

The cleaning position of the dry ice blasting assembly with respect tothe nozzle 120 of the droplet generator 115 is programmed by thecontroller 1500 according to different cleaning modes. For example, thecleaning position may be programmed in a horizontal configuration of thechamber 105. After positioning the blasting nozzle 1150 to the cleaningposition (the horizontal configuration of the chamber 105), theextendable positioner 1180 stops moving. The dry ice particles 1082 thenclean the droplet generator 115 until the end of a cleaning time 1070.

As shown in FIG. 7 , the dry ice blasting assembly 1000 further includesa supporting member 1300 that includes a blasting compressor 1320 and ablasting pump 1340. The blasting compressor 1320 compresses a liquidform of carbon dioxide from the blaster carbon dioxide (CO₂) inlet 1130into the solid dry ice particles 1082, and pressurizes air taken in fromthe blasting air inlet 1120. In some embodiments, the inlets 1120, 1130and the blasting compressor 1320 are located outside of the chamber 105.In some embodiments, the blasting compressor 1320 supplies liquefiednitrogen (LN₂) with a pressure of about 2,000 kPa to about 50,000 kPa tothe dry ice transport port 1360. In certain embodiments, the blastingcompressor 1320 generates the dry ice particles 1082 with a density ofabout 1,000 g/cm3 to about 200,000 g/cm3. In such configuration, the dryice particles 1082 impact the nozzle 120 of the droplet generator 115 ata pressure of range of about 1 kPa to about 1000 kPa, and clean thedroplet generator 115. In some embodiments, an ultrasonic generator maybe used with the dry ice particles 1082 in a frequency of about 20 kHzto about 20 MHz.

In some embodiments, the dry ice blasting assembly 1000 further includesthe blasting pump 1340 for mixing dry ice particles 1082 and thepressurized air stream 1084, and for pressurizing the mixture 1086. Thepressurized dry ice particles 1080 are ejected from the dry ice blastingassembly 1000, i.e., the blasting nozzle 1150, and directed at thedroplet generator nozzle 120. In some embodiments, the flow rate of thepressurized air stream 1084 for the pressurized dry ice particles 1080is in a range from about 0.5 liters per minute to about 500 liters perminute. Such pressurized dry ice particles 1080 impact the nozzle 120 ofthe droplet generator 115 at a pressure in a range from about 1 kPa toabout 1000 kPa depending on the diameter of the blasting nozzle 1150,the flow rate of the pressurized air stream 1084 for the pressurized dryice particles 1080, and a distance between the blasting nozzle 1150and/or the droplet generator nozzle 120.

In some embodiments, the blasting nozzle 1150 has a diameter in a rangefrom about 10 μm to about 10 mm for dispensing pressurized dry iceparticles 1080, including the dry ice particles 1082 and the pressurizedair stream 1084.

The impact of the dry ice particles 1082 particles creates microscopicshock waves 1090 that help breakdown the tin oxide particulate cloggingthe droplet generator nozzle 120 in some embodiments. Additionally,because the dry ice particles 1082 immediately sublimate from solid togas as it impacts the droplet generator nozzle 120, additional solidparticulate waste is not left behind. The gaseous carbon dioxide 1088 isrelatively inert and does not react with any of the material of othercomponents in the chamber 105. Moreover, gaseous carbon dioxide 1088 canbe easily removed from the chamber 105 along with the air as the chamber105 is being evacuated.

An embodiment of the present disclosure provides a droplet generator 115cleaning method, including: providing a selectively attachable dry iceblasting assembly 1000. Ejecting the pressured dry ice particles 1080toward the nozzle 120 of the droplet generator 115 at the pressure ofrange of about 1 kPa to about 1000 kPa during a cleaning operationwherein the pressured dry ice particles 1080 impact the nozzle 120 ofthe droplet generator 115. At a pressure in the range of about 1 kPa toabout 1000 kPa, the impact of the dry ice particles do not cause damageto the nozzle 120 of the droplet generator 115, the temperature of theresidual material 1022 adhered to the nozzle 120 impacted by the dry iceparticles is rapidly lowered, the residual material 1022 is embrittled,and a crack is formed between the residual material 1022 and the dropletgenerator 115. Next, a portion of the dry ice particles 1082 whichsubsequently impact the droplet generator 115 enters the crack 1024, andthe dry ice particles 1082 then rapidly sublimate into gas. Because thevolume of the gaseous carbon dioxide 1088 is greater than an originalvolume of the dry ice particles 1082, the gaseous carbon dioxide 1088further enlarges the crack 1024 and reduces adhesion of the residualmaterial 1022. In some embodiments, as additional dry ice particles 1082further impact the residual material, the residual material 1022 isseparated from the nozzle 120 of the droplet generator 115, therebycleaning the nozzle 120 of the droplet generator 115.

By using the foregoing method, the residual material 1022 clogging thenozzle can be effectively removed. In addition, the dry ice particles1082 are not corrosive, and thus, would not corrode the dropletgenerator 115. Moreover, the dry ice particles 1082 will rapidlysublimate into carbon dioxide gas after impact, and thus, acontamination medium will not be generated. Thus, without contaminationor damaging the nozzle 120 of the droplet generator 115, the dropletgenerator 115 is cleaned and maintenance and servicing time and/or costare reduced in embodiments of the disclosure.

An exemplary cleaning procedure according to embodiments of thedisclosure is as follows: firstly, the blasting air inlet 1120transports the compressed air into the blasting mixer 1140, and due tothe compressed air, the liquid carbon dioxide is converted into the dryice particles 1082. The blasting mixer 1140 transports the dry iceparticles 1082 via the dry ice transport port 1360 to the blastingnozzle 1150. The blasting nozzle 1150 directs the pressured dry iceparticles 1080 to the nozzle 120 of the droplet generator 115 at apressure in the range of about 1 kPa to about 1000 kPa and a flow rateof the pressurized air stream 1084 for the pressurized dry ice particles1080 in a range from about 0.5 liters per minute to about 500 liters perminute, to clean the droplet generator 115. In this cleaning procedure,the blasting member 1100 directs the pressurized dry ice particles 1080to the nozzle 120 of the droplet generator 115 and the microscopic shockwaves are generated by the dry ice particles 1082 causing the residualmaterial 1022 to be removed from the nozzle 120 of the droplet generator115. The exhaust member 1200 collects the residual material 1022separated from the nozzle 120 of the droplet generator 115 and thegaseous carbon dioxide 1088 sublimated from the dry ice particles 1082through an exhaust line 1220. Thereby, the cleaning effect is furtherenhanced by the microscopic shock waves 1090, and contamination insidethe chamber 105 is reduced in some embodiments.

An embodiment of the disclosure, as shown in FIG. 8 of a flow chart, isa method S100 of cleaning an extreme ultra violet (EUV) radiation sourceapparatus. In operation S110, pressurized dry ice particles includingdry ice particles and the pressurized air stream from the dry icesupporting member of the dry ice blasting assembly are formed. Inoperation S120, the pressurized dry ice particles are ejected throughthe blasting nozzle toward residual material at the nozzle of the targetdroplet generator. In operation S130, the residual material from thetarget droplet generator are removed. In operation S140, the residualmaterial and sublimated gaseous carbon dioxide from the pressurized dryice particles are collected, thereby the EUV radiation source apparatusis cleaned.

In another embodiment, the cleaning system for an extreme ultra violet(EUV) radiation source apparatus includes a target droplet generator forgenerating a metal droplet, a dry ice blasting assembly, and a chamberthat encloses at least the target droplet generator and the dry iceblasting assembly. The dry ice blasting assembly comprises a blastingdevice, an exhausting device, and a supporting device.

As shown in the flow chart of FIG. 9 , another embodiment of thedisclosure is a method S200 of cleaning an extreme ultra violet (EUV)radiation source apparatus. In operation S210, a target dropletgenerator for generating a metal droplet is provided within a chamber.In operation S220, the vacuum in the chamber 105 is removed to allowoxygen to enter the chamber. In operation S230, the oxygen within thechamber reacts with the residual material on the target dropletgenerator. In operation S240, a dry ice blasting assembly having ablasting nozzle and a dry ice supporting member is provided inside thechamber. In operation S250, pressurized dry ice particles including dryice particles and the pressurized air stream from the dry ice supportingmember are formed. In operation S260, the pressurized dry ice particlesare ejected through the blasting nozzle toward the residual material atthe nozzle of the target droplet generator. In operation S270, theresidual material from the target droplet generator are removed. Inoperation S280, the residual material and sublimated gaseous carbondioxide from the pressurized dry ice particles are collected.

Embodiments of the present disclosure provide the benefit of reducingdowntime during maintenance and servicing of EUVL tools. The design ofthe cleaning system and dry ice blasting assembly allows for fastermaintenance with reduced servicing time. The adaptation of the cleaningsystem allows an improved process resulting in reduced manpower requiredto perform the maintenance, and an increased output of conformingservicing items of the EUVL tools—both of which ultimately result in acost-savings. As such, the EUVL tool is more efficiently used. However,it will be understood that not all advantages have been necessarilydiscussed herein, no particular advantage is required for allembodiments or examples, and other embodiments or examples may offerdifferent advantages.

In a particular embodiment, an extreme ultra violet (EUV) radiationsource apparatus includes a target droplet generator for generating ametal droplet, a dry ice blasting assembly, a chamber enclosing at leastthe target droplet generator and the dry ice blasting assembly. The EUVradiation source apparatus also includes a controller communicating withthe dry ice blasting assembly and target droplet generator. The dry iceblasting assembly of the EUV radiation source apparatus is selectivelyattachable to and extendable from the chamber. The dry ice blastingassembly of the EUV radiation source apparatus also includes a blastingdevice, an exhaust device, and a supporting device.

An embodiment of the disclosure is a method of cleaning an extreme ultraviolet (EUV) radiation source apparatus, in which the EUV radiationsource apparatus comprises a target droplet generator for generating ametal droplet within a chamber, and a dry ice blasting assembly having ablasting nozzle disposed inside the chamber and a dry ice supportingmember. The method includes forming pressurized dry ice particlesincluding dry ice particles and a pressurized air stream from the dryice supporting member of the dry ice blasting assembly, ejecting thepressurized dry ice particles through the blasting nozzle towardresidual material at a nozzle of the target droplet generator, removingthe residual material from the target droplet generator, and collectingthe residual material and sublimated gaseous carbon dioxide from thepressurized dry ice particles. In an embodiment, the cleaning methodincludes positioning the blasting nozzle with respect to the residualmaterial by an extendable positioner. In an embodiment, the cleaningmethod includes oscillating the pressure of the pressurized dry iceparticles. In an embodiment, the cleaning method includes monitoring theresidual material on the droplet generator, adjusting valves of theblasting pump when an amount of the residual material in the dropletgenerator is more than a threshold amount, and regulating the operatingparameters of the blasting compressor and the blasting pump. In anembodiment, the cleaning method includes positioning a blasting memberof the dry ice blasting assembly in the chamber. In an embodiment, thecleaning method includes positioning an exhaust member of the dry iceblasting assembly in the chamber. In an embodiment, the flow rate of thepressurized dry ice particles ejected through the blasting nozzle is ina range from 0.5 liters per minute to 500 liters per minute. In anembodiment, the pressure of the pressurized dry ice particles ejectedthrough the blasting nozzle is in a range of 1 kPa to 1000 kPa at thenozzle. In an embodiment, the pressurized dry ice particles ejectedthrough the blasting nozzle have a diameter in a range from about 10 μmto about 10 mm.

Another embodiment of the disclosure is a method of cleaning an extremeultra violet (EUV) radiation source apparatus, includes providing atarget droplet generator for generating a metal droplet within achamber. The vacuum of the chamber is removed allowing residual materialon the nozzle of the target droplet generator to react with oxygen. Adry ice blasting assembly having a blasting nozzle and a dry icesupporting member is provided inside the chamber. Pressurized dry iceparticles including dry ice particles and a pressurized air stream fromthe dry ice supporting member are formed. The pressurized dry iceparticles are ejected through the blasting nozzle toward the residualmaterial at the nozzle of the target droplet generator. The residualmaterial are removed from the target droplet generator, and collectedthe residual material and sublimated gaseous carbon dioxide from thepressurized dry ice particles. In an embodiment, the cleaning methodincludes regulating the cleaning using a controller configured to:monitor the residual material on the droplet generator, and compare anamount of the residual material in the droplet generator with athreshold amount to remove the residual material by the pressurized dryice particles. In an embodiment, the cleaning method includes stoppingthe ejecting the pressurized dry ice particles when the amount of theresidual material in the droplet generator is below the thresholdamount.

Another embodiment of the disclosure is a cleaning system for an extremeultra violet (EUV) radiation source apparatus that includes a targetdroplet generator for generating a metal droplet, a dry ice blastingassembly and a chamber enclosing at least the target droplet generatorand the dry ice blasting assembly. In an embodiment, the dry iceblasting assembly of the cleaning system for the (EUV) radiation sourceapparatus includes a blasting device, an exhausting device, and asupporting device. In an embodiment, the dry ice blasting assembly ofthe cleaning system includes a monitoring device for monitoring residualmaterial on the target droplet generator. In an embodiment, the blastingmember of the cleaning system includes a blasting air inlet, a blastercarbon dioxide inlet, a blasting mixer and a blasting nozzle. In anembodiment, the blasting nozzle of the cleaning system includes apulsation insert and a directional insert. In an embodiment, thesupporting member of the cleaning system includes a blasting compressor.In an embodiment, the supporting member includes a blasting pump. In anembodiment, the blasting member includes an extendable positioner. In anembodiment, the cleaning system includes a controller configured tomonitor residual material on a nozzle of the droplet generator, adjustvalves of the blasting pump when an amount of the residual material inthe droplet generator is more than a threshold amount, and regulateejecting parameters of the blasting compressor and the blasting pump,when pressurized dry ice particles are ejected from the blasting nozzle.

Another embodiment of the disclosure is an extreme ultra violet (EUV)radiation source apparatus, including: a target droplet generator forgenerating a metal droplet, a dry ice blasting assembly, a chamberenclosing at least the target droplet generator and the dry ice blastingassembly, and a controller communicating with the dry ice blastingassembly and target droplet generator. The dry ice blasting assembly ofthe EUV radiation source is selectively attachable to and extendablefrom the chamber. The dry ice blasting assembly includes a blastingdevice, an exhaust device, and a supporting device. In an embodiment,the controller of the EUV radiation source is configured to monitorresidual material in the droplet generator and adjust valves of theblasting pump when an amount of the residual material in the dropletgenerator is more than a threshold amount, and regulate ejectingparameters by operating the blasting compressor and the blasting pumpwhen pressurized dry ice particles are ejected from a blasting nozzle.In an embodiment, the EUV radiation source includes a pulsation insertand a directional insert in the blasting nozzle.

The foregoing outlines features of several embodiments or examples sothat those skilled in the art may better understand the aspects of thepresent disclosure. Those skilled in the art should appreciate that theymay readily use the present disclosure as a basis for designing ormodifying other processes and structures for carrying out the samepurposes and/or achieving the same advantages of the embodiments orexamples introduced herein. Those skilled in the art should also realizethat such equivalent constructions do not depart from the spirit andscope of the present disclosure, and that they may make various changes,substitutions, and alterations herein without departing from the spiritand scope of the present disclosure.

What is claimed is:
 1. A method for removing residual material from anextreme ultraviolet (EUV) radiation source, the method comprising:generating target droplets of a given material in a droplet generatorthrough a nozzle of the droplet generator; monitoring residual materialon the droplet generator to measure an amount of the residual material;and removing the residual material by ejecting pressurized dry iceparticles based on the measured amount of the residual material.
 2. Themethod of claim 1, wherein microscopic shock waves by the pressurizeddry ice particles remove the residual material from the target dropletgenerator.
 3. The method of claim 1, further comprising: forming thepressurized dry ice particles.
 4. The method of claim 3, furthercomprising: forming a pressurized air stream from a cleaner supportingmember.
 5. The method of claim 1, wherein removing the residual materialfurther comprises collecting the residual material and sublimatedgaseous carbon dioxide from the pressurized dry ice particles.
 6. Themethod of claim 1, further comprising: adjusting valves of a blastingpump when an amount of the residual material in the droplet generator ismore than a threshold amount; and regulating operating parameters of ablasting compressor and the blasting pump.
 7. The method of claim 1,wherein a flow rate of the pressurized dry ice particles ejected througha cleaner blasting nozzle is in a range from 0.5 liters per minute to500 liters per minute.
 8. The method of claim 1, wherein a pressure ofthe pressurized dry ice particles ejected through a cleaner blastingnozzle is in a range of 1 kPa to 1000 kPa at the nozzle.
 9. The methodof claim 1, wherein the pressurized dry ice particles ejected through acleaner blasting nozzle have a diameter in a range from about 10 μm toabout 10 mm.
 10. A method for removing residual material in an extremeultraviolet (EUV) source, the method comprising: generating targetdroplets of a given material in a droplet generator through a nozzle ofthe droplet generator; removing the residual material by a cleanerblasting assembly having a cleaner blasting nozzle; and adjusting apressure of pressurized dry ice particles of the cleaner blastingassembly based on an amount of the residual material removed.
 11. Themethod of claim 10, further comprising an exhaust device configured tocollect the residual material.
 12. The method of claim 10, furthercomprising: adjusting a pulsation insert configured to generate apulsation of pressurized air stream of the cleaner blasting nozzle. 13.The method of claim 10, further comprising: adjusting a supportingmember including a blasting compressor.
 14. The method of claim 10,further comprising: adjusting valves of a blasting pump when the amountof the residual material in the droplet generator is more than athreshold amount.
 15. The method of claim 10, further comprising:regulating ejecting parameters of a blasting compressor and the blastingpump, when pressurized dry ice particles are ejected from a cleanerblasting nozzle.
 16. The method of claim 10, wherein the cleanerblasting assembly is selectively attachable to and extendable from achamber.
 17. A cleaning apparatus for an extreme ultraviolet (EUV)radiation source, comprising: a cleaner blasting assembly having acleaner blasting nozzle to remove residual material from a targetdroplet generator; an imaging device configured to monitor the residualmaterial on the droplet generator; and a controller communicating withthe cleaner blasting assembly and the imaging device configured toadjust cleaning modes and position of the cleaner blasting assembly toenhance the cleaning effect.
 18. The cleaning apparatus of claim 17,wherein the controller regulates ejecting parameters of a blastingcompressor and the blasting pump, when pressurized dry ice particles areejected from the blasting nozzle.
 19. The cleaning apparatus of claim18, wherein the controller stops the ejection of the pressurized dry iceparticles when an amount of the residual material on the dropletgenerator is below a threshold amount.
 20. The cleaning apparatus ofclaim 17, wherein the controller further include an exhaust device tocollect the residual material and sublimated gaseous carbon dioxide frompressurized dry ice particles.